Trace fossils Flashcards
What is another name for trace fossils?
Ichnofossils
What can trace fossils be used as?
Palaeoenvironmental indicators
What is endogenic trace fossils?
Made/ found within the rock (type of preservation)
What is epirelief trace fossil preservation?
Preserved on the top of beds
What is hyporelief?
Located at the base of beds
What is full relief?
Located within beds
What are exogenic traces?
Made on the sediment surface
How are full relief trace fossils preserved?
burrow preserved in 3d
What is another name for epirelief and hyporelief?
semi relief
Where is hyporelief most common?
Interbedded sands and muds
Where is an example of hyporelief?
Aberystwyth Grits (Silurian)
What are natural casts, true track, undertracks? (trace fossils)
Natural - made by infilling of original track
True - actual imprint
Undertrack - dent in sediment by animal pressure
What is the bias with trace fossils/ undertracks?
Bias towards heavier that can leave a greater impression
What is an example of undertrack preservation?
Sauropod footprints in the Morrison Formation Colorado
What problems are associated with trace fossil identification?
Single organism can produce many trace fossils
Different organism can produce similar trace fossils
What do invertebrate trace fossils names tend to reflect?
Morphology of trace (shape and ornamentation)
What can be used to describe the morphology of trace fossils?
Ichnogenus and Ichnospecies
How many trace fossils are produced by the Uca (modern day fiddler crab)?
4 traces
What are the trace fossils produced by Uca?
Psilonchnus - domichnion (living burrow)
Diplichnites - repichnion (walking trail)
Pascichnion - grazing trail
Coprolites - feacal pellets
What is the name for the resting trace? (cubchnia)
Rusophycus
What is the problem associated with identifying resting traces?
Originally thought just trilobites hunkering down on sediment but found other organisms can produce aswell
What are some examples of organisms which can produce resting fossils?
Polychaete worms
Snails
Brachiopod shrimps
Trilobites
What is repichnia?
walking or crawling trace
What is an example of a crawling trace?
Cruziana - Ordovician Anzaldo Fm Bolivia
What is an example of domichnion? (living burrow)
Arenicolites
What do arenicolites produce?
U shaped burrows which makes a worm cast and depression
What do arenicolite worm burrows do to the rock chemistry?
Anoxic rock is made oxygen rich by when oxygenated water is pulled into the sediment
What is the difference between diplocraterion and arenicorlite?
Scars of where burrow used to be (spreite)
What is the name of the burrow behaviour of diplocraterion?
fugichnia - escape trace
What is the ichnogenus and ichnospecies name of diplocraterion?
Diplocraterion yoyo
Why is the name diplocraterion yoyo given?
Due to the changing position of the organism burrow due to erosion and deposition to avoid burial or exposure
What is pascichnia? (trace fossil)
surface feeding trace
What is an example of pascichnia?
Helminthoidea
What is fodinichnia? (trace fossil)
Mining feeding trace
What is an example of where fodinichnia can be found?
Chondrites in hardening sandstones from Ordovician Colorado
or
Zoophycos
Where is fodinichnia produced in the sediment layers?
close to the water sediment interface
Why is the pattern distribution in swooping motions for fodinichnia?
To avoid eating poop
Maximise exploited sediment
What are chondrites produced by?
A worm
What is agrichnia? (trace fossils)
Cultivation trace (hexagon pattern used to cultivate algae)
What is an example of agrichnia trace?
Paleodictyon
What trace fossil is the base of the cambrian defined by?
Phycodes
What are hycodes followed by?
Trace fossil assemblage containing Rusophycos and Cruziana
What are phycodes like?
Looping structure
What is the prominence of Rusophycos and Cruziana appearing so early in the fossil record?
They precede trilobite body fossils
What is tiering in trace fossils?
How many layers are exploited by burrowers
What has happened to tiering over time?
Mid Ordovician 3 tiers
Remains like that till Early Jurassic
Then large diversification as deep seafloor exploited leading to 9 tiers in late cretaceous
What are Thalassonoids?
Wide shape burrow produced by shrimp typical of littoral deposits (shore face)
What are the names of trace fossil communities? (ichnofacies)
Nereites
Zoophycos
Cruziana
Skolithos
Scoyenia
Glossifungites
What trace burrows make up the Nereite ichnofacie?
Spiroraphe
Lorenzinla
Chondrites
Paleodictyon
Nereites
Cosmorhaphe
What are Nereite ichnofacies like?
Absence of vertical burrows
Deepwater environments
Found in muds (deposited from suspension)
Mud and siltstones of distal turbidites
What traces make up Zoophycos ichnofacies?
Phycosiphon
Zoophycos
Spirophyton
What are the characteristics of Zoophycos ichnofacies? (distribution, conditions)
Complex fodinichnia
Deep traces - Thalassinoides
Tiered arrangement
Abyssal to shallow continental shelf
Might occur in normal background conditions
What traces are found in the Cruziana ichnofacie?
Asteriacites
Cruziana
Rhizocorallium
Aulichnites
Thalassinoides
Chondrites
Telchichus
Arenicolites
Rossella
Planolites
What are the characteristics of Cruziana ichnofacies? (orientation, environment and position)
Horizontal and vertical burrows
Mid and distal continental shelf
Below normal wave base (storm activity potential)
What traces make up the Skolithos ichnofacies?
Ophiomorpha
Diplocraterion
Skolithos
Monocraterion
What are the characteristics of skolithos ichnofacies? (orientation, environment and sediment)
Low diversity vertical burrows
Intertidal situations
Sporadic sediment deposition (shifting sand and intertidal environments, storm sand sheets and top of turbidity flows)
What are the trace fossil ichnofacies thought to be controlled by?
Sediment type
Water depth
Rate of deposition
What is a sub trace fossil community?
Scoyenia ichnofacie
Glossifungite ichnofacie
What traces make up the scoyenia ichnofacie?
Scoyenia
Acorichnus
Cruziana
Skolithos
What traces make up the Glossifungite ichnofacie?
Thalassinoides
Bivalve boring
Polychaete burrows
Rhizocorallium
Psilonichus
What are the characteristics of Glossifungite ichnofacies? (sediment, environment)
Sediment firm but not lithified (mud/ silt)
Low energy salt marshes, mud bars, high intertidal flats or shallow marine)
What are the characteristics of scoyenia ichnofacies? (orientation, sediment)
Horizontal (occasionally vertical)
Fluvial and lacustrine sediment
Aeolian sands and paleosols
What are some examples of substrate dependant trace fossils?
Teredolites (wood)
Trypanites (limestone)
What traces make up the trypanites ichnofacies?
Echinoid grooves
Barnacle borings
Sponge borings
Polychaete worms
Bivalve boring
Sypuncullid boring
What are the controls on distribution of trace fossil communities?
Average grain size of sediment
Sediment stability
Water content
Chemical conditions
How does average grain size affect trace fossil community distribution?
Affect sediment ingesting burrowers
Organisms require particular sediment size to line burrow
Filter feeders avoid fine sediments
How does water content affect trace fossil community distribution?
Affects consistency of sediment
What are black shales have through to represent on the sea floor?
Soupy sediment cant burrow in
How do chemical conditions affect trace fossil community distribution?
Oxygen levels are particularly important, with trace fossils being absent in totally
anoxic environments
